Commercially available tetracycline preparations may contain significant amounts of degradation products of the antibiotic. Some of these degradation products are inactive in vivo (4-epi-tetracycline and anhydrotetracycline) and one is actually toxic (4-epi- anydrotetracycline) causing renal dysfunction. Because of the large number of preparations on the market and the wide use of the antibiotic, one mission of this proposal is to determine the incidence of the occurrence of these degradation products and a quantitation of the amounts of each in commercial preparations intercepted at the point of normal dispensing from active stock. In this way the potential health hazard to the public may be settled. To overcome this problem, the methodology used in this study utilizes high pressure liquid chromatography to separate and quantify components of the mixture quickly, easily, and accurately. A second mission of the study is to characterize the pathways by which 4-epi-anhydrotetracycline can form. Understanding these mechanisms will provide information with regard to methods of preparation and storage of the antibiotic that assure the public that the medication used is safe and potent. The formation of anhydrotetracycline and 4-epi-tetracycline from tetracycline has been previously studied, but the formation of 4-epi-anhydrotetracycline from 4-epi-tetracycline and anhydrotetracycline has not. To study these latter reactions high pressure liquid chromatography, spectrophotometry and circular dichroism represent convenient tools to kinetically measure the rates.